Study of the browning and gelation kinetics in a concentrated sheep milk and sucrose system

Browning and gelation kinetics of a sheep milk and sucrose model system with 70% total solids (simulating dulce de leche) and the influence of temperature and sucrose content on this process were studied. The Kubelka–Munk index and subjective heat stability tests were used to monitor nonenzymatic browning and to determine gelation time. Browning and gelation processes showed different kinetics where gelation was shown to occur much faster than browning. Both independent variables (temperature and sucrose content) had a significant influence in both processes, where temperature had the higher impact.     

Influence of temperature on crystallization of lactose in ice-cream

Sandiness in ice-cream due to lactose crystallization can still be a problem in many circumstances. Lactose crystallization occurs in ice-cream as the unfrozen phase becomes supersaturated. However, the effects of storage temperature and temperature fluctuations on lactose crystallization have not been very well quantified. In this work, an accelerated storage apparatus was used to determine the effects of thermal fluctuations (from ±0.01°C to ±2.0°C), at several mean storage temperatures (from −5.0 to −20.0°C), on the onset of lactose nucleation and subsequent crystal growth in a standard vanilla ice-cream. the induction time for nucleation initially decreased as temperature was lowered (for temperature oscillations of ±1.0°C), until a minimum induction time of 3 h was found between −10.0 and −12.0°C. Further decreases in storage temperature caused the induction time to increase. the induction time for nucleation increased as the extent of temperature fluctuations increased, from 0.01 to 2.0°C, while initial lactose crystal growth rate showed the opposite trend. the initial growth rate increased as temperature decreased between −5.0 and −10.0°C, but then decreased for temperatures below −10.0°C. At −20.0°C lactose crystals grew very slowly. At −10.0°C the rate of growth decreased with increasing amplitude of temperature oscillations.     

Isothermal batch crystallization of alpha-lactose: A kinetic model combining mutarotation,nucleation and growth steps

A kinetic model combining first-order differential equations of the three consecutive steps of lactose crystallization, i.e., mutarotation, nucleation and crystal growth rate, was developed. Numerical solutions successfully fitted the variations of crystal mass growth rate as a function of lactose concentration during unseeded isothermal batch crystallization, at different initial lactose concentrations and temperatures. The model allowed the induction phase and the influence of seeding to be simulated by taking into account the dependency of crystal growth rate on total crystal surface area and, consequently, on nucleation rate. The proposed model highlights the large influence of the mutarotation step, even in unseeded crystallization kinetics. The effects of high lactose supersaturations that prevail at industrial scale during whey powder manufacturing and the effects of alkaline pH (9.5) on lactose crystallization kinetic were successfully predicted.     

Crystallization kinetics of lactose in sytems co-lyofilized with trehalose. Analysis by differential scanning calorimetry

The objective of the present work was to study by differential scanning calorimetry phase/state transitions in model systems of amorphous lactose and lactose co-lyophilized with trehalose. The obtained parameters, such as glass transition temperatures (T_g) and enthalpies of crystallization were employed to test the applicability of different proposed models to predict the behavior of these systems. Thermograms of low moisture lactose–trehalose mixtures showed only one glass transition temperature indicating that compatibility exists between both sugars. The increase of trehalose concentration in the mixture promoted a delay of lactose crystallization in isothermal runs, and of the crystallization temperature (T_cr) in dynamic experiments. The presence of trehalose delayed lactose crystallization, without affecting the T_g value. Several factors (thermodynamic, geometric, kinetics) may modify the molecular environment in the combined systems, affecting nucleation and/or crystal growth. Three models [Arrhenius, Williams–Landel–Ferry (WLF) and Vogel–Tamman–Fulcher (VTF)] were used to study the temperature dependence of the crystallization time. Although experimental points were fitted fairly well by all these models in the range of temperature from 14 to 59 °C above T_g value, the VTF equation appears to apply better for sugars.     

Crystallization Kinetics and X-ray Diffraction of Crystals Formed in Amorphous Lactose, Trehalose, and Lactose/Trehalose Mixtures

ABSTRACT: Effects of storage time and relative humidity on crystallization kinetics and crystal forms produced from freeze-dried amorphous lactose, trehalose, and a lactose/trehalose mixture were compared. Samples were exposed to 4 different relative water vapor pressure (RVP) (44.1%, 54.5%, 65.6%, 76.1%) environments at room temperature. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage humidity. Lactose crystallized as α-lactose monohydrate, β-anhydrous, and anhydrous forms of α- and β-lactose in molar ratios of 5:3 and 4:1 in lactose and lactose/trehalose systems. Trehalose seemed to crystallize as a mixture of trehalose dihydrate and anhydrate in trehalose and lactose/trehalose systems. The crystal forms in a mixture of lactose and trehalose did not seem to be affected by the component sugars, but crystallization of the component sugars was delayed. Time-dependent crystallization of lactose and trehalose in the lactose-trehalose mixture could be modeled using the Avrami equation. The results indicated that crystallization data are important in modeling of crystallization phenomena and predicting stability of lactose and trehalose-containing food and pharmaceutical materials. Keywords: crystallization, lactose, trehalose, crystal form, X-ray diffraction     

Whey protein aggregation under shear conditions – effects of pH-value and removal of calcium

The effects of pH-value and a reduction in calcium content on the kinetics of whey protein denaturation and the aggregation behaviour, under shear in a scraped surface heat exchanger, were examined. The denaturation rate of β-lactoglobulin at 80 °C is considerably retarded as the pH-value decreases from pH 6.7 to 4.5. Aggregates which are produced under shear between pH 4 and 5.5 reveal a small particle size (<5 μm) irrespective of the lactose content and the heating temperature. This is attributed to the low reactivity of the thiol groups and the small net charge of the proteins in this pH-range. At a reduced calcium concentration the heat- and shear-treatment resulted in a gritty structure with large rubber-like particles. These are not to be taken as primary whey protein aggregates but as fragments of a fine-stranded gel.     

Glass transition and crystallization behaviour of freeze-dried lactose-salt mixtures

Glass transition temperatures were determined for dehydrated lactose/salt mixtures with various water contents and water activities, and state diagrams were established. Crystallization behaviour was studied for pure amorphous lactose stored at various relative water vapour pressures (RVP). Furthermore, glass transitions temperatures and time-dependent lactose crystallization of freeze-dried lactose and lactose/CaCl₂, lactose/NaCl, lactose/MgCl₂ and lactose/KCl mixtures in molar ratios of 9:1 were determined. Glass transition temperatures (T_g) of lactose powder as determined by differential scanning calorimetry (DSC) was lower than that of lactose/CaCl₂ (9:1)_, and lactose/MgCl₂ (9:1), but it was slightly higher than the T_g of lactose/NaCl (9:1), and lactose/KCl (9:1). Lactose/KCl had the lowest glass transition temperature, but it had about the same crystallization temperature as lactose/NaCl, and lactose/MgCl₂. The glass transition temperatures decreased as water contents increased. The critical water contents and water activities at 23 °C were predicted using data on glass transition temperature and water sorption. Pure lactose had a different critical water activity and water content from lactose/salt mixtures. The critical values of lactose/CaCl₂ (9:1) were the highest. Loss of sorbed water, indicating lactose crystallization, was observed in lactose and lactose/salt mixtures stored above the critical RVP.     

Nucleation of lactose using continuous orifice flow

This paper describes two methods used to produce a constant supply of super-saturated lactose solution with nuclei already present, required as the feed stream for a new design of a continuous crystalliser. Both methods involve cooling a hot saturated lactose solution to super-saturation and then passing it through an orifice or applying mechanical agitation to initiate nucleation. Orifice Reynolds number (Re) of 500 and 1000 and wait times subsequent to cooling of 0 and 1 h were used. Wait time and Re had no effect on nuclei numbers, but a wait time at an orifice Re of 1000 increased crystal size and decreased the span of the crystal size distribution, suggesting that these conditions produced faster growing crystals. In experiments with nucleation by mechanical agitation followed by dilution, crystal numbers were several orders of magnitude lower than for orifice nucleation, and resulted in a small span.     

Stability of Concentrated,Decolorized, Deionized Hydrolyzed Whey Permeate

Four separate lots of whey permeate from ultrafiltration of sweet cheese whey were deionized and decolorized to remove whey-like flavor and color, treated with β-galactosidase to hydrolyze lactose, and concentrated. Variables introduced were levels of lactose hydrolysis and total solids; storage temperature; order of deionization, hydrolysis, and decolorization processes; and use of a 75°C posthydrolysis heat treatment. Each batch was evaluated for microbial stability, resistance to crystallization, and flavor after 3 mo storage at 37°C.Concentration of permeate to less than 60% total solids resulted in microbial instability, and greater than 85% lactose hydrolysis resulted in galactose or lactose crystallization. Heating to 75°C and storing at elevated temperatures (up to 37°C) minimized crystallization. However, heating to 75°C accelerated browning. Flavor evaluation of browned samples suggested that caramelization rather than Maillard browning was the principal factor. Decolorizing with activated carbon after hydrolysis made no difference to the amount of sugar crystallization.Lactose hydrolysis improved the stability of concentrated, decolorized, deionized hydrolyzed whey permeate. The syrup with longest storage stability was decolorized, 90% deionized, contained 85 to 90% hydrolyzed lactose, was concentrated to 65% total solids, heated to 75°C following concentration, and stored at 30°C.     

平面蒸发法制备氯化钠颗粒

氯化钠是工业生产和人类生活重要的无机盐产品。研究通过平面蒸发的方法制备了氯化钠结晶,考察了不同的蒸发温度、结晶时间以及添加剂种类对氯化钠粒径分布的影响。结果表明,随着温度从50℃到70℃和时间从3.5 h到6.5 h的增加,大颗粒氯化钠呈现增加的趋势。MgCl2、CaCl2和ZnCl2的加入有助于氯化钠晶粒的生长,并且对氯化钠的结晶形态有影响。     

Water sorption and time-dependent crystallization behaviour of freeze-dried lactose-salt mixtures

Water sorption properties of freeze-dried lactose, lactose/CaCl₂, lactose/NaCl, lactose/MgCl₂, and lactose/KCl mixtures in their molar ratio of (9:1) were investigated. Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were used to model water sorption properties. Water is known to function as a plasticizer, depressing the glass transition and facilitating crystallization. Crystallization in the present study resulted in loss of sorbed water from lactose. The crystallization of pure lactose and lactose/salt mixtures was observed at RVP?44.0% within 24 h. At RVP?54.4% water contents were higher in lactose/CaCl₂ and lactose/MgCl₂ mixtures than in pure lactose, lactose/NaCl, and lactose/KCl.Water content in pure lactose after crystallization was ?5.0%, suggesting that lactose crystallized as a mixture of α-lactose monohydrate and various anhydrous forms of α/β-lactose crystals. Anhydrous lactose/CaCl₂ and lactose/MgCl₂ had higher glass transition temperatures than lactose, but other salts (NaCl and KCl) with lactose gave lower glass transition than amorphous lactose. It seems that bivalent salts in mixtures with lactose gave a higher T_g than smaller monovalent ions. Salts delayed lactose crystallization. The effect on lactose crystallization was highest with calcium chloride (CaCl₂) and lowest with potassium chloride (KCl). It seems that different salts interacted with lactose to different extents. For water sorption, GAB model gave a better fit than BET model. Water sorption and time-dependent crystallization properties of lactose/salt mixtures should be considered in manufacturing and storage of dairy-based dehydrated materials.     

Investigation of breakage behavior and its effects on spray-dried agglomerated whey protein-lactose powders: Effect of protein and lactose contents

Particle breakage of dairy powders occurs easily during many processes, reducing the powder functionality. The characteristics of particles and the applied stress from processing conditions on the particles are 2 main factors that can be manipulated to reduce breakage. In this study, we explored the effect of whey protein and lactose contents on dynamic breakage in agglomerated whey protein-lactose powders to provide useful information, in terms of particle characteristics, for controlling unwanted dairy powder breakage. A series of model agglomerates with different whey protein:lactose ratios were produced under the same spray-drying conditions, through a pilot plant trial. We evaluated physical characteristics, composition, and structure of samples; analyzed dynamic breakage under different mechanical stresses; and investigated the rehydration and water adsorption properties of model powders before and after breakage. The particle size and irregularity of agglomerates with more lactose was significantly higher than of samples that contained more protein. This resulted in higher particle breakage during dynamic breakage for samples with more lactose. The breakage of agglomerates was affected by the moisture content of powders and fatigue, where particle breakage happens when mechanical loads, lower than the strength of particles, occur multiple times. Breakage changed the morphology and surface composition of particles and decreased particle size. It also decreased the dispersibility of powders and increased the wetting time of wettable samples but decreased the wetting time of powders with poor wettability. Breakage accelerated time-dependent crystallization and decreased the crystallization temperature but did not affect the glass transition temperature of samples. Thus, under the same drying conditions, composition of powders significantly affected breakage, mainly by altering the physical properties of their particles, which resulted in deteriorated functionality.     

Recovery of lactose from simulated delactosed whey permeate by a low-temperature crystallization process

Delactosed whey permeate is the mother liquor/by-product of lactose manufacture, but it still contains around 20 wt% lactose. The high mineral content, stickiness, and hygroscopic behavior prevent further recovery of lactose in the manufacturing process. Therefore, its use is currently limited to low-value applications such as cattle feed, and more often it is seen as waste. This study investigates a new separation technique operating at sub-zero conditions. At low temperature, precipitation of calcium phosphate is expected to be reduced and the lower solubility at sub-zero temperature makes it possible to recover a large portion of the lactose. We found that lactose could be crystallized at sub-zero conditions. The crystals had a tomahawk morphology and an average size of 23 and 31 µm. In the first 24 h, the amount of calcium phosphate precipitated was limited, whereas the lactose concentration was already close to saturation. The overall rate of crystallization was increased compared with the crystals recovered from a pure lactose solution. Mutarotation was rate limiting in the pure system but it did not limit the crystallization of lactose from delactosed whey permeate. This resulted in faster crystallization; after 24 h the yield was 85%.     

木糖醇介稳区宽度与晶体生长速率测定

用激光散射法测定纯木糖醇水溶液和含有山梨醇和葡萄糖杂质的木糖醇水溶液的结晶介稳区宽度;在介稳区内测得不同结晶温度下纯木糖醇溶液中过饱和度对晶体生长速率的影响,同时研究杂质的添加对木糖醇结晶生长速率的影响。结果表明：相同结晶温度下,生长速率随过饱和度的增大而增大;在相同结晶温度和过饱和度下,木糖醇水溶液中分别加入山梨醇和葡萄糖杂质导致生长速率下降,并随杂质含量的增大而下降,山梨醇对晶体生长的抑制作用比葡萄糖更明显。     

Online ice crystal size measurements during sorbet freezing by means of the focused beam reflectance measurement (FBRM) technology. Influence of operating conditions

In ice cream and sorbet manufacturing small ice crystals are desired to deliver a product with a smooth texture and good palatability. This research studied the influence of the operating conditions on the ice crystal size and the draw temperature of the sorbet during the freezing process. The evolution of ice crystal size was tracked with the focused beam reflectance measurement (FBRM) technique, which uses an in situ sensor that makes it possible to monitor online the chord length distribution (CLD) of ice crystals in sorbets containing up to 40% of ice. The refrigerant fluid temperature had the most significant influence on the mean ice crystal chord length, followed by the dasher speed, whereas the mix flow rate had no significant influence. A decrease in the refrigerant fluid temperature led to a reduction in ice crystal size, due to the growth of more small ice crystals left behind on the scraped wall from previous scrapings. Increasing the dasher speed slightly reduced the mean ice crystal chord length, due to the production of new small ice nuclei by secondary nucleation. For a given refrigerant fluid temperature and dasher speed, low mix flow rates resulted in lower draw temperatures, due to the fact that the product remains in contact with the freezer wall longer. High dasher speeds warmed the product slightly, due to the dissipation of frictional energy in the product, the effect of which was in part moderated by the improvement in the heat transfer coefficient between the product and the freezer wall.     

Effect of cooling rate on lipid crystallization in oil-in-water emulsions

The effect of cooling rate on the destabilization of oil-in-water (o/w) emulsions was studied as a function of oil content (20% and 40% o/w), homogenization conditions, and crystallization temperatures (10, 5, 0, ?5 and ?10 °C). The lipid phase was a mixture of anhydrous milk fat and soybean oil, and whey protein was used as the emulsifier. Differential scanning calorimetry was used to analyze the crystallization and melting behaviors; while a vertical scan macroscopic analyzer measured the physicochemical stability. Slow cooling rate increased the stability of emulsions with 20% oil. In addition, slow cooling promoted the onset of crystallization and delayed crystal growth. These effects were more significant in emulsions formulated with 20% oil and formulated under processing conditions that resulted in bigger droplet sizes (～0.9 μm).     

椰子油在温度梯度场中定向结晶动力学

目的：了解椰子油在温度梯度场中的结晶行为过程,优化结晶参数（如结晶温度、熔点、冷却速率、搅拌速率等）,以获得具有特种性能的分提产品。方法：以椰子油为原料,采用分级熔融结晶的方法,考察不同温度梯度场下椰子油的定向结晶行为。结果：Avrami方程可以基本适用椰子油的结晶过程,但在结晶后期,均会出现部分偏离。同时,椰子油结晶过程中,其晶体生长方式以及晶体形状随着温度的不同均会有所变化。结论：温度梯度法可以有效得到所需的椰子油分提产品。     

Evaluating the crystallization of lactose at different cooling rates from milk and whey permeates in terms of crystal yield and purity

The cooling rate of supersaturated lactose solution is one of the important parameters determining the yield and size distribution of lactose crystals. The influence of increasing cooling rate on lactose crystallization and quality of lactose crystals was evaluated in concentrated solutions prepared from deproteinized whey powder (DPW) and milk permeate powder (MPP). Concentrated permeates (DPW and MPP) with 60% (wt/wt) total solids were prepared by reconstituting permeate powders in water at 80°C for 2 h for lactose dissolution. Three cooling rates, 0.04°C/min (slow), 0.06°C/min (medium), and 0.08°C/min (fast) were studied in duplicate. A common rapid cooling step (80 to 60°C at 0.5°C/min) followed by slow, medium, and fast cooling rates were applied as per the experimental design from 60 to 20°C. After crystallization, the crystal slurry was centrifuged, washed with cold water, and dried. The dried lactose crystals were weighed to calculate the lactose yield. Final mean particle chord lengths were measured at the end of crystallization using focused beam reflectance measurement for slow, medium, and fast cooling rates, and observed to be not significantly different for DPW (27–33 µm) and MPP (31–34 µm) concentrates. Similarly, the lactose yield for slow, medium, and fast cooling rates in the DPW and MPP concentrates were in the range of 71 to 73% and 76 to 81%, respectively, and no significant difference between the 3 cooling rates was found. Qualitative analysis of dried lactose crystals exhibited no noticeable differences in the crystal purity with increasing cooling rate. This study evaluated the possibility of reducing the crystallization times by 8 h compared with current industrial practice without compromising the crystal yield and quality.